Mother knows best: plant polyploidy affects feeding and oviposition preference of the alligator weed biological control agent, Agasicles hygrophila

Alligator weed (Alternanthera philoxeroides (Martius) Grisebach) is an amphibious invasive plant native to South America. It is an allopolyploid that, in Argentina, possess two cytotypes, tetraploids and hexaploids. In the exotic range, the plant is biologically controlled with flea beetle Agasicles hygrophila Selman and Vogt but with different levels of success. The genotype of host plant is an important factor that needs to be considered in biological control programs. We studied how alligator weed ploidy level affects the oviposition preferences of A. hygrophila and its relation with female feeding preference, egg survival and larval performance in its native range. Females recognized the different ploidy levels of alligator weed and preferred to lay eggs on hexaploids than tetraploids. This choice positively affected larval performance and may be explained by the preference–performance hypothesis in this case for different plant cytotypes. Polyploidy should be considered in evaluating and prioritising biological control agents.